Spark Arrestor Solutions

Discussion in 'Trials' started by motobene, May 23, 2017.

  1. motobene

    motobene Motoing for 46 years

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    Just implemented a pricey Sherco spark arrestor solution, the 1.25" aluminum weldment adapter and 32mm machined aluminum Sparky on a customer bike. I say 'pricey' because both bought together aren't cheap.

    If you need a spark arrestor for a Sherco-Scorpa, the compound angle of the muffler end makes adapting a spark arrestor without a custom adapter difficult.

    Got both from RYP.

    The adapter does not fit into the muffler exit hole but lines up with it. Flow is thus not resisted much, so the negative influence on jetting is minimized.

    The 32mm Sparky is 0.01" oversize on the adapter, whereas the adapter is sourced from tubing extruded to inch nominal outside diameter. The fit is quite sloppy, with the clamp screw distorting the clamp to get to a point of retention.

    My fix was to cut some 0.008" aluminum flashing to lay fit between adapter shaft and Sparky bore. The fit becomes right when a single cut piece covers about 35% of the area. The clamp screw then easily retains the spark arrestor.

    The adapter doesn't fit quite flush on the muffler end because the muffler has a slight angled projection round the exit tube. I used a stainless washer under the adapter flange at the bottom screw to shim the gap to provide better support. I also sealed the adapter to the plastic with clear Silicone 1 rubber, which is good to 500 degrees. I hope I like the sound on my 250 with the Sparky off, so I can just leave an adapter on.

    I plan to machine my own adapter to 32mm. It will include the flange so there won't be a weld on mine. Mine also won't need shimming. But I'll mount it like the weldment with two screws.

    The weldment adapter screws on with two small countersunk-head, stainless-steel Phillips screws. I lined it up with the muffler hole and muffler facets, then drilled two 0.085" holes, which allowed the screws to form full threads.

    I prefer to safety wire mine so it vibrated or knocked off in a crash the items will dangle instead of disappear into another universe. I use some Malin Co. 0.025" stainless steel wire looped through the Sparky clamp screw slot and affixed to the top inside muffler tip screw.

    My previous solution was my own adapter with a Sparky. It was more restrictive, however, being on a tube that fit inside the muffler exit hole instead of lining up with the hole.

    Please show us your solutions!
    #1
  2. motobene

    motobene Motoing for 46 years

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    Some pix IMG_20170522_173702654.jpg IMG_20170522_173615215.jpg .
    #2
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  3. motobene

    motobene Motoing for 46 years

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    Here you can see my previous solution among parts for the present solution.

    Note the piece of aluminum flashing I used to fix the fit disparity.
    IMG_20170519_155610821.jpg
    #3
    LemmeTry likes this.
  4. Huzband

    Huzband Team Dirt

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    Looks pretty trick, but it won't comply with my clubs lease rules. Unfortunately I'm on the board, so trying to squeak something by isn't an option. I'm still trying to decide whether or not to take off the end cap and fashion something inside, or just not ride at our property. Which would suck because it's only 9 miles from my house.
    #4
  5. TXNMGUY

    TXNMGUY dirt dobber

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    Why would that not comply?
    #5
  6. laser17

    laser17 Long timer

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    Sweet looking welds Bene. I know who I'm sending my next weld job too.
    #6
  7. lineaway

    lineaway Long timer

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    Actually there is no spark arrestors made for trials bikes. They all are illegal. Ever since Wes quit making them.
    #7
  8. ridenm

    ridenm Long timer

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    Line's correct as far as I have been able to verify. A spark arrester is only truly legal if it has been submitted to USFS and certified. The most up-to-date list I've found is here: https://www.fs.fed.us/t-d/programs/fire/spark_arrester_guides/_assets/2012_OHV.pdf. For some reason the 2015 update sheet is not available right now.
    When you look as a Spanish Fly screen it says "USFS-type" and it doesn't have any of the regulatory language.
    #8
  9. Tomb Raider

    Tomb Raider Been here awhile

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    He was out when I was looking, RYP. I like the mounting better then what I ended up getting. Mine fits inside the end, she's got a Snap POP to her so some back pressure was added. Seems to run fine tho.
    #9
  10. Huzband

    Huzband Team Dirt

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    Our lease property rules, which are dictated by the land owner & their lawyers, states that spark arrestors must be contained within the silencer, not attached to the end cap as shown. Mine already has a screen attached similar to what motobene fabed so I ran it by our VP to get a second opinion. He said what I would've said, rulz iz rulz.
    #10
  11. ridenm

    ridenm Long timer

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    So what are your club members running?
    #11
  12. Huzband

    Huzband Team Dirt

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    Silencers with USFS approved spark arrestors. I should clarify that it's not a trials club, in fact I'm the only one with a trials bike.
    #12
  13. LemmeTry

    LemmeTry Over-thinker...

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    That stinks! But if you take the end cap off and make something work inside, it still won't satisfy them since it doesn't say USFS on the silencer, will it?
    #13
  14. ridenm

    ridenm Long timer

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    Thanks for the clarification.
    #14
  15. Huzband

    Huzband Team Dirt

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    Ha, actually it will. When we inspect bikes (and I'm one of the inspectors) we drop a probe into the silencer. If it stops, the bike passes, but we don't pull out our magnifying glass & look for a USFS stamp. So if I put the same screen 6 inches upstream I'll be golden. :D
    #15
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  16. LemmeTry

    LemmeTry Over-thinker...

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    Oh, that's not so bad then. :thumb
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  17. Tomb Raider

    Tomb Raider Been here awhile

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    I've run poker runs in the Woods and the USFS inspected along with the DNR for Sparky's and a ADD ON was OK here in the Great North West. A DRZ 400 has a end cap with a screen in it and that's the Sparky part. I've taken mine off like many for flow. Funny how state to state dictates.
    #17
  18. motomofo

    motomofo Been here awhile

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    I have a buddy who took the Krizman-style spark arrestor out of an old stock KTM EXC two stroke muffler (the hockey stick one), and installed it in his Beta Evo muffler. Then he cut the USFS info off, and riveted it on. Easily passed the poke test, just as legal as anything else available, and probably works better, too. Screen type spark arrestors are such a bad choice for two strokes, anyway.

    It's funny how spark arrestors are such a big deal, especially in the enduro bike world... but exposed, red hot, glowing header pipes on modern four strokes are just fine. Seen a few fires started by this, but no concern is given.
    #18
  19. ridenm

    ridenm Long timer

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    As are street-legal vehicles (cars and trucks) with modern catalytic converters running 600-700 def F.
    A County vehicle started a fire in the tall, dry grass of the bosque here a few years ago.
    #19
  20. motomofo

    motomofo Been here awhile

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    Actually, now that you mention it... a city vehicle did the same thing in a tall, dry field here a couple summers ago.
    #20